An ever present machine shop problem is to locate a reference point on the workpiece relative to the center of a drill spindle or the like. The problem exists whatever may be the scale of the machine shop operation, from a large scale production shop utilizing digital or computer control of worktables, to a small home or experimental shop. Excellent but very expensive viewer microscope equipment exists.
Small job shops have used simple pointed instruments placed in the chuck of the machine. Such pointed instruments, when moved into position, obscure the reference mark on the workpiece which, of course, an optical instrument does not. If the pointed instrument has a flexible shaft and if the reference mark is an indentation or small hole, then concentricity can be verified if the instrument with its point in the indentation or hole does not wiggle or laterally vibrate when the machine is power rotated. An optical instrument has precision measurement capabilities that the mechanical instrument does not have. For example, an optical instrument, by projecting scale markings around the optical center, can assist in finding a point exactly half way between two references. The primary object of the present invention is to provide very simple optical instrument which can be priced so low that its purchase unquestionably can be justified for use in any shop, however small.